I believe that I may have been hitting the following ‘bug’/issue:
bug-ad-blockers-break-circleci-ui-due-to-hard-optimizely-requirement
In spite of having seen that report, and taking action (e.g. disabling adblock), nothing appeared to change. Several days on however (and an accidental Firefox browser restart later), the ‘Workflows’ section now (correctly?!) populates with something useful and re-running the builds from there has allowed me to progress.
I’d guess that some Firefox cache path wasn’t cleared… although I could have sworn I’d Ctrl-F5ed the page (maybe that shortcut is changed …or rather it’s just ineffective!)